Acoustic diaphragm



- March 1, 1932. H. STENSEL 1,8 1,901

ACOUSTIC DIAPHRAGM Filed June 16. 1930 Fig. 1.

Inventor: Heinrich Stensel His Attorney m an acoustic device of this 1 which Patented Mar. 1, 1932 UNITED STATES PATENT 'UOFFICE HEINRICH STENSEL, 0F BERLIN-STEGLITZ, GERMANY, ASSIGNOR TC GENERAL ELEC TRIC COMPANY, A CCRPORA'I'ION ACOUSTIC DIAPHRAGM p Application filed J'une 16, 1930, Serial No. 461,321, and in Germany July 19, 1929.

My invention relates to acoustic. devices comprising diaphragms, particularly of the cone type, and its object is the provision of character for interconversion of sound and electric impulses in which distortion of the impulses is avoided.

Heretofore acoustic devices such as loud speakers have included a cone shaped diaphragm, which is comparatively rigid and tends to vibrate as a whole. As compared with fiat diaphragms thecone shaped type offers the advantage that harmonic vibrations are avoided to a great extentthus eliminating one important source of distortion. I have found, however, that the cone type diaphragm offers certain other disadvantages, the existence of which make clear.

why it has not been possible heretofore to produce sound without distortion by means of this type of diaphragm notwithstanding that by the use of such diaphragms harmonic vibrations are substantially eliminated. Experiments I have made indicate that certain interference effects are produced in the use of diaphragms of the cone type even thoughthese diaphragms are rigid and therefore vibrate as a whole. I find that the explanation of the existence of these interference effects is to be found in the fact that the cone shaped diaphragm has a certain depth, the diaphragm being necessarily of a diameter and depth suflicient to obtain therefrom sound wave emission which will answer practical requirements. In accordance with my invention, the above stated interference effects are obviated by providing substantially equal sound paths which extend from th e diaphragm to the plane of the circumference of the diaphragm or the plane of emergence of sound waves from said diaphragm. These sound 7 paths respectively conduct sound waves originating from various points of the surface of the cone. To this end my invention provides a sound-guiding element disposed within the space Which is enclosed by the diaphragm, the element occupying this space almost completely so that only a small clearance space exists between the surface of the diaphragm and the element. The sound- I guiding element is provided with ductsinto from the following and through which the sound waves pass, so that sound waves originating from various points of the surface of the diaphragm and therefore having in certain cases a difference in pitch will have covered the same distance within the element when they emerge from theelement. The flat surface bounding this sound-guiding element may lie within the plane of sound wave emergence of the diaphragm. In certain cases, however, the sound guiding element may be so dimensioned that its boundary surface is at acertain distance from the plane of sound wave emergence of the diaphragm.

My invention will be better understooddescription when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a partially cross sectional View of anacoustic device in accordance with the invention and Fig. 2 is a lan view thereof. i

In the gures, a diaphragm element 10 having the form of the frustum of a cone is provided at its outer circumference with a. ring of flexible material clamped in a groove between two holding rings 11 and 12-. The top of the diaphragm is connected to'a pin 13 carried on a magnetic structure 14, the connection being made through the medium of resilient means, such for example as a perforated cardboard disk 15. A coil supporting element 16 on which may be wound an actuating coil (not shown) is connected to the top of the diaphragm.

Owing to the depth of the diaphragm, in-

terference phenomena are produced when the daphragm is vibrated. They take effect more particularly along the axis thereof and are detrimental espectially for the reproduc-.

tion of high frequencies. Complete interference will occur between two sound waves terference effect, I provide in accordanceis equal to an odd multiple thereof.

of the paper,

with the invention a truncated cone 20, of wood or the like, disposed within the space enclosed by the diaphragm 10. This truncated cone 20 is carried on pin 13 but is otherwise clear of the surface of the diaphragm being maintained in proper position close to the diaphragm in any suitable manner as by a ring 32 fastened to the edge of the cone and clamped between the rings 11, 12. Gone 20 constitutes a sound-guiding element having a large number of ducts, of which only a few are shown in order to avoid complicating the drawing. These ducts 2122, 23-24, 25-26, 2728, 29-30 lead to the flat boundary surface 31 of the soundguiding element 20 and are preferably of substantially equal length, so that the sound paths for the sound waves originating at the surface of diaphragm 10 and entering the ducts across the narrow space between the diaphragm and the cone 20 are all of substantially equal length as far as the boundary surface 31. The duct 2122 starts at the point 21 on the conical surface of the cone 20 close to the smaller base thereof and continues, in a direction approximately parallel to the axis of the cone, to a point not far from the center of the circular boundary surface 31. The duct 21-22 opens on his boundary surface at the point 22.

Since the cone 20 is shown in side elevation in Fig. 1 of the drawings, in this figure, there fore, the lower opening 21 of duct ill-22 appears in full line as an ellipse on the conical surface of the cone 20, whereas the duct itself, within the cone, is shown in dotted line extending upwardly from the lower opening 21 to the upper opening 22 in the circular boundary surface 31, the exact location of the upper opening 22 on the surface 31 being shown in Fig. 2.

In Fig. 2, since the cone 20 is shown in top plan new, the cone 20 being behind the plane the inner or lower opening 21, shown as located near the lower edge of the cone in the side elevational view of Fig. 1, appears in dotted line in the central portion of Fig. 2. The duct 21, 22 thence extends, toward the plane of the paper as shown in dotted line in Fig. 2, to the upper or outer opening 22. The upper opening 22 shown in full line in Fig. 2 is formed in the flat circular boundary surface 31, and not far from the center of this surface.

The duct 293O is similar to duct 21-22 but the lower end of duct 29-30 is located, as shown in full line in the side elevational view of Fig. 1 and in dotted line in the top plan view of Fig. 2, at a point 29 on the conical surface of cone 20 approximately threefourths of the distance between the smaller base of the cone and the larger base or boundary surface 31. The duct 29--30 extends, from its inner or lower opening 29, diagonally with respect to the cone bases, and

upwardly to the upper opening 30 which is located near the periphery of the boundary surface 31 of cone 20. The duct 29-3O is so sloped with reference to the duct 21-22, which is approximately parallel to the axis of cone 20, that the sound paths formed by the two ducts are of substantially equal length.

The other ducts illustrated in the drawings are so disposed that their inner or lower openings 23, 25, 27 are located in the conical surface of cone 20 at progressively greater distances from the opening 21 of duct 21, 22 in the direction of lower opening 29 of duct 29-30, and that their upper or outer openings 2 1, 26, 28 are located in the boundary surface 31 of cone 20 at progressively greater distances, between upper openings 22 and 30 of duct 2122 and 2930 respectively, from the center of the surface 31.

Ducts 2321, 25-2-3, and 2.*'-28 are of progressively greater slopes with reference to the base of cone 2(), the slopes being between the slope of inner duct 2122 and the slope of outer duct 29-30. The slopes of ducts 23-2 1, and 27-28 are so chosen that these intermediate ducts are of substantially the same length as the inner duct 21-22 and outer duct 29-.30. There is, therefore, no difference in pitch between sound waves originating, for example, at two points 21 and 29 of the diaphragm surface and no detrimental interference effects occur between these sound waves.

The above described device in accordance with my invention makes it possible in general to compel sound waves originating at various points of the surface of the diaphragm to follow paths of predetermined length. The device may, therefore, be used in certain cases for producing an intentional difference in pitch in order to give the frequency curve of the loud speak-er a particular shape, for exan'iple, for compensating a resonance point. It is within the scope of the invention to fill the space enclosed by the diaphragm with a sound-guiding element composed of a number of sections in order that the ducts may be given the required length with greater facility. The device may also be used for recording sound vibrations, or for microphonic purposes.

lVhat I claim as new and desire to secure by Letters Patent of the United States is:

1. In an acoustic device, a diaphragm of substantial depth, and means comprising sound wave ducts of predetermined length disposed within said diaphragm to prevent interference of sound waves originating at different points of said diaphragm.

2. In an acoustic device, a conical diaphragm, and means comprising sound wave ducts of substantially equal length disposed within said diaphragm to prevent interference of sound Waves originating at different points of said diaphragm.

In an acoustic device, a conical diaphragm and means to conduct sound waves originating at different points of said diaphragm through paths of predetermined length to the plane of emergence of sound Waves from said diaphragm.

4:. In an acoustic device, a diaphragm of substantial depth and a plurality of sound Wave ducts of predetermined length leading from different points of said diaphragm to points adjacent to the plane of the circumference of said diaphragm.

5. In an acoustic device, a cone shaped diaphragm and a plurality of sound ducts of substantially equal length ferent points of said diaphragm to the plane of the circumference of said diaphragm.

6. In an acoustic device, a conical diaphragm, a sound-guiding element disposed Within said diaphragm and a plurality of sound Wave ducts formed Within said element.

7. In an acoustic device, a conical diaphragm, a sound-guiding element disposed Within said diaphragm and closely adjacent the Wall thereof, and a plurality of sound Wave ducts of substant'ally equal length formed Within said element to prevent interference of sound Waves originating at different points of said diaphragm.

In an acoustic device, a conical diaphragm, a sound-gulding element dlsposed Within said diaphragm, closely adjacent the wall thereof and having a boundary Wall,- and a plurality of sound Wave ducts of pre-' determined length leading from difi'erent points of said element adjacent said diaphragm to said boundary Wall.

In an acoustic device, a conical diaphragm, a sound-guiding element disposed Within said diaphragm closely adjacent the Wall thereof and having a boundary Wall in the plane of the circumference of said diaphragm and a plurality of sound Wave ducts of substantially equal length leading from different points of said element adjacent said diaphragm to said boundary wall.

In Witness whereof, I have hereunto set my hand this 22nd day of May, 1930.

HEINRICH STENSEL.

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